A thyristor starter includes a converter configured to convert a first three-phase AC power to a DC power, a DC reactor configured to smooth a direct current, and an inverter configured to convert the DC power supplied from the converter via the DC reactor to a second three-phase AC power which is supplied to a synchronous motor. The thyristor starter further includes an AC voltage detector configured to detect a first three-phase AC voltage input to the converter and a second three-phase AC voltage output from the inverter, and a control circuit configured to control the converter and the inverter on the basis of a detection result from the AC voltage detector. By controlling the second three-phase AC power, it is possible to start the synchronous motor from a stopped state and make it rotate at a predetermined rotating speed (for example, see Japanese Patent Laying-Open No. 2003-61380 (PTD 1)).